Mobile data demand is growing explosively. Some industry and academic experts predict a 1000-fold demand increase by 2020 [1]. In order to offer the 1000× increase in data rates and throughput, small cells densely deployed underlying the conventional homogeneous macrocells are emerging as a promising candidate for the fifth generation (5G) mobile broadband [2]. This new network deployment is usually referred to as heterogeneous cellular networks (HCNs). However, with the increase of the number of small cells deployed, the backhaul for small cells becomes a significant challenge [2], [3]. Although fiber based backhaul offers large bandwidth, it is costly, inflexible, and time-consuming to connect the densely deployed small cells. In contrast, wireless backhaul is more cost-effective, flexible, and easier to deploy [3]. With huge bandwidth available, wireless backhaul in mmWave bands, such as the 60 GHz band and E-band (71-76 GHz and 81-86 GHz), provides several-Gbps data rates and can be a promising backhaul solution for small cells.